The interactions between a tumor and its local environment are critical to tumor development and progression, and ultimately to tumor metastasis. Most of our current knowledge of the signaling molecules secreted by tumor cells is based on in vitro studies that have largely ignored the dynamics of the in vivo tumor environment. The overall goal of this proposal is to study the dynamics of signaling peptide and protein secretion by several tumor types (fibrosarcoma, breast, prostate and myeloma) implanted in bone. In the R21 portion of the application we propose to combine a novel in vivo microperfusion procedure, which allows sampling of extracellular fluid from solid tumors over time, with new mass spectrometry methods allowing identification of proteins in mixtures. The R21 phase will be used to further develop MALDI-TOF, ESI-Q-TOF and ESI-MS/MS procedures and to optimize conditions for maximum detection and for identification of proteins and peptides in bone tumor microperfusates. The interactions of various tumor types with the unique micro-environment found in bone will be studied in the proposed R33 phase by analyzing the secretion of selected as well as unidentified proteins produced by breast, prostate and myeloma tumors over time. By permitting the in vivo identification of an array of peptides and proteins present in tumor extracellular fluid over time, this novel microperfusion approach will provide the opportunity to characterize the extracellular peptides and proteins secreted by different bone tumor types which are involved in the growth, progression, latency and metastasis of these tumors. The data obtained from these studies will facilitate cancer detection and diagnosis as well as define new targets or therapeutic and preventative agents.